1. Field of the Invention
The present invention is related to a pixel and a liquid crystal display (LCD) panel. More particularly, the present invention is related to an active device array substrate and a pixel structure having a storage capacitor.
2. Description of Related Art
With advantages of high definition, small volume, light weight, low voltage drive, low power consumption, and a wide range of applications, an LCD has replaced a cathode ray tube (CRT) display to become the mainstream display product in the next generation. In general, an LCD panel includes an active device array substrate, a color filter substrate, and a liquid crystal layer.
Specifically, the active device array substrate includes a plurality of thin film transistors (TFTs) arranged in array and pixel electrodes respectively corresponding to the TFTs, for example. Here, the TFTs serve as switches for turning an LCD unit on or off. Additionally, each pixel structure is individually controlled by a certain scan line and a certain data line. Through enabling the certain scan line and the certain data line by supplying appropriate operational voltages, data corresponding to the certain pixel structure can be displayed. Practically, to ensure the holding of the operational voltage applied to each of the pixel structures and to further improve display quality, the scan line or a common line is often covered by a part of a pixel electrode in each of the pixel structures, so as to form a storage capacitor.
FIG. 1A is a top view of a conventional pixel structure, while FIG. 1B is a schematic view alone a cross-sectional line A-B depicted in FIG. 1A. Referring to FIGS. 1A and 1B, in a conventional pixel structure 10, a storage capacitor C is mainly formed by coupling a common line 30 and a pixel electrode 40 disposed above the common line 30. In addition, a gate insulator 50 and a passivation layer 60 are formed between the common line 30 and the pixel electrode 40, so as to form the storage capacitor C having an MII-type structure composed of Metal layer/Insulator/Indium Tin Oxide (ITO) layer. The storage capacitor C is generally used for stabilizing a data voltage of the pixel structure 10 and for improving the display quality of the LCD. The data voltage of the pixel structure 10 can be stabilized to a better extent when a storage capacitance Cst reaches a relatively great value.
Referring to FIG. 1B, a method for increasing the storage capacitance Cst of the pixel structure 10 is performed by extending an overlapping area of the common line 30 and the pixel electrode 40, whereas an aperture of the pixels is prone to be reduced by performing said method. As such, luminance of images that are displayed by the LCD may be insufficient.
On the other hand, the storage capacitance Cst of the pixel structure 10 can also be increased by extending an area of an electrode or reducing a thickness of the insulator. In detail, even though the storage capacitance Cst can be increased by extending the overlapping area of the common line 30 and the pixel electrode 40, the aperture of the pixels is inevitably reduced, thus negatively affecting the image display effect and the image display quality.
Given that it is intended to increase the storage capacitance Cst in the conventional pixel structure 10 without sacrificing the aperture, the total thickness of the gate insulator 50 and the passivation layer 60 must be reduced, such that the storage capacitance Cst in the conventional pixel structure 10 can be increased. It is also possible for the storage capacitor C of the pixel structure 10 to have an increased value by performing an etching process on a channel layer, so as to simultaneously reduce the thickness of the gate insulator 50. Nevertheless, the gate insulator 50 of the storage capacitor C is apt to be etched unevenly, which deteriorates device characteristics of the storage capacitor C.